Free-radical curable, styrene-containing resins are well-known to those skilled in the art and widely available from commercial sources. Such resins include, for example, styrene-containing unsaturated polyesters, vinyl esters and urethane acrylates or methacrylates. All of these resins are alpha, beta-ethylenically unsaturated carboxylates. These resins, especially unsaturated polyesters, can be easily adapted to many common thermoset molding techniques for the construction and transportation industries, including the manufacture of parts for automobiles, trucks, boats, machine housings and household items such as bath fixtures. Another application for such resins is in the construction of tanks, piping and process equipment for chemicals and chemical waste such as underground gasoline storage tanks. These resins are selected as a replacement for metals such as steel, stainless steel, aluminum and bronze because of their ability to resist corrosion and chemical attack. Therefore, it is desirable to provide such resins which, when molded, have good toughness, impact and adhesion properties as well as hydrolytic, thermal and chemical resistance.
However, styrene emissions associated with the manufacture of free-radical curable, styrene-containing resins are now limited by regulations promulgated in 1989 by the U.S. Occupational Safety and Health Administration (OSHA). According to these regulations, manufacturers in many industries must reduce workplace styrene emissions from 100 parts per million to 50 parts per million. Environmental requirements issued by the South Coast Air Quality Management District (SCAOMD) in California apply to such resins and mandate that styrene emissions must be less than 60 grams per square meter of styrene by a paint can lid test described below.
In order to meet new environmental regulations, manufacturers of styrene-containing resins might either reduce the styrene monomer content of resins or suppress emissions from existing styrene-containing compositions. The problem with lowering the styrene content is that styrene functions to provide a workable viscosity of the resin and to crosslink with the unsaturation in the resin, such as a polyester polymer backbone. Therefore, lowering the amount of styrene in the resin will have an impact on other properties.
Several approaches to lowering styrene emissions have been tested without success. One approach is to lower the molecular weight of the resin in order to reduce the amount of styrene needed to obtain a workable resin viscosity. The problem with this approach is that the flexural strength of the resin is greatly decreased, particularly when tested after exposure to high temperatures or chemical exposure. Another approach to reducing emissions in unsaturated polyester resins is to substitute part of the styrene with another additive such as hydroxyethyl methacrylate or methyl methacrylate. However, neither of these substitutes works as well as styrene in most applications. For example, chemical resistance of a polyester resin is lower in a hydroxyethyl methacrylate additive system. Similarly, vinyl toluene has been tested as a substitute for styrene in unsaturated polyesters. While it appeared that the styrene emissions and interlaminar adhesion were acceptable, this system could not be used at workable viscosity levels which would also meet styrene emission requirements.
The general object of this invention is to provide free-radical curable, styrene-containing resin compositions having reduced styrene emissions. It is another object of the invention to provide such resins with reduced styrene emissions without significantly affecting the preparation, processing and physical properties of the resins when used in molding processes. It is another object to provide a simple, inexpensive method for making such resin compositions. It is yet another object to provide molded articles having good physical properties which are made from such compositions. Other objects appear hereinafter.
These and other objects are achieved by the addition of a small amount of a paraffin wax and a fluorocarbon surfactant to a free-radical curable, styrene-containing polymerizable resin composition. Unexpectedly, it has been found that compositions containing a paraffin wax and a fluorocarbon surfactant have lower styrene emissions without significantly affecting preparation, processing, and physical properties, particularly chemical and hydrolytic resistance and interlaminar adhesion of the cured or polymerized resin compositions.